1. Field of the Invention
The present invention relates to an electrification removing component which is employed for preventing parts from electrical breakage by a rapid electric discharge which is caused in handling an electrified electronics related parts and the like.
2. Discussion of Background
There is a case wherein, in manufacturing steps of an electronics related part including a semiconductor device, the part is provided with an electric charge by a direct electrification or by an induced electrification. When the electrified part contacts an electric conductive material such as a metal and the like having a small electric resistance, a rapid discharge of an electric charge is often caused and the part is electrically broken (dielectric breakdown) by the discharge. It is an important problem to prevent the breakage of the part caused by this discharge.
As a ceramics having an electric conductive property, an electrically conductive ceramics of alumina added with an element of iron group and an element of 2A group or an element of 3A group, is disclosed, for instance, in Japanese Examined Patent Publication No. 54630/1992, and a sintered body of silicon nitride which is capable of working with an electric discharge machining and provided with a small specific resistivity, wherein a nitride or a carbide of Ti, Ta, Zr, and Hf is mixed with silicon carbide, in Japanese Examined Patent Publication No. 43699/1990. As a ceramics for the purpose of preventing electrification, a titania ceramics, a zirconia ceramics, a silicon nitride ceramics, or a silicon carbide ceramics, having a specific resistance of 10.sup.2 through 10.sup.6 .OMEGA..cm, which is attached to a holding part of metallic tweezers, is disclosed in Japanese Examined Utility Model Publication No. 2303/1993.
Further, a suction chuck is proposed in Japanese Unexamined Utility Model Publication No. 114441/1990, which is one for attracting a part for working or for measuring physical properties, and which prevents dusts from adhering on its suction face due to electrification, by employing ceramics having a specific resistivity of 10 through 10.sup.5 .OMEGA..cm. A vacuum conveyer (vacuum chuck) is proposed in Japanese Examined Patent Publication No. 42418/1986, of which surface contacting a silicon wafer is composed of a high-purity silicon carbide (of which surface resistivity is normally in a range of 10.sup.3 through 10.sup.4 .OMEGA./cm.sup.2) and which does not contaminate an object to be handled.
However, these materials do not provide reliability for components employed in removing electrification by the following reasons. The first reason is that a voltage of static electricity charged on a part and the like is often as high as above 2000 V, and it has been revealed that a material with a level of specific resistivity of not more than 10.sup.2 .OMEGA..cm is not sufficient for protecting the part from an electric breakage when the discharge is caused and for removing the electric charge without destructing the part.
It is considered pertinent for a way of representing an electric resistance of a material for removing electrification by the surface resistivity in view of a mode of utilizing the material. However, no unified representation is currently adopted. In case of a uniform material, with respect to the surface resistivity and the specific resistivity, both generally agree with each other in most cases, although there is a case wherein measured values of these are different by a decimal digit. It is considered from these knowledges, that the surface resistivity which is suitable for the purpose of removing electrification is to be around 10 .sup.6 through 10.sup.10 .OMEGA./cm.sup.2. However, a suitable material showing the surface resistivity in this range has not been found in a material having a single composition.
On the other hand, a floor sheet for removing electrification wherein a plastics is kneaded with carbon powders and the like, has been reduced into practice. However, plastics are apt to deteriorate when a strong cleaning is performed thereon and give out dusts when they are worn. When the worn plastics contact an object to be handled, the object may be contaminated by the dusts. On the other hand, generally, ceramics are chemically stable, excellent in refractoriness and corrosion resistance and provided with an advantage wherein they are hard and difficult to wear. Therefore, ceramics are preferable materials for a component directly contacting an object to be handled that abhors contamination.
However, ceramics is provided with drawbacks wherein it is a brittle material and is easy to fracture, and much labor and cost are required for working it into a product; for instance, it is necessary to perform grinding by a diamond grinding wheel in working it into a required shape.
Further, in employing the ceramics for removing electrification for a component for removing electrification, it is necessary to electrically connect the ceramics for removing electrification to an electric conductive material that is connected to the ground. When the surface resistivity of the ceramics for removing electrification is as large as not less than 10.sup.6 .OMEGA./cm.sup.2, and an electric conductive material such as a lead wire simply contacts the ceramics for removing electrification, the contact resistance is apt to be very large and unstable, and therefore, it is not possible to remove with certainty a charged static electricity from an object to be handled when the ceramics is used as the material for removing electrification.